Method of treating tin bearing materials



Patented Mar. 4, 1947 TREATING 'rrIN BEARING A MATERIALS Irving E. Mus'kat, Plainfield, N. J.

No Drawing.

-24 Claims.

This invention is directed to the recovery of tin from tin ores, including concentrated and unconcentrated ores, preferably from'those containing 5 per centby weight or more of'tin.

This application is 'a continuation-impart of my copending applicationSerial No.469j373, filed December, 17, 1942.

In accordance with "the present invention I have found 'that'tin maybe recovered efficiently and at relatively low cost from tin oresor concentratesby'a process involving a reaction of the tin content thereof in a reduced state with an aqueous solution of an alkali metal hydroxide.

In the practice of .the process "herein contemplated a tin ore in a finely divided stateisheate'd. in the presence of aquan'tity of a reducing agent capable of reducing tin oxide to metallic tin, such as carbon,'coal, 'la'mp'black, petroleum coke, carbon monoxidanatur'a'l gas,*hydrogen, etc., for a time requiredand at a predtermine'dtemperature to convertthe tin content .of the ore into a state capable of reacting with asolution of an alkali metal hydroxide. Thereafter the treated ore is subjected, under .controlled conditions, to

the action of an aqueous alkaline solution, preferably an aqueous solution of an alkali metal hydroXide such as sodium orpotassium hydroxide. In order to achieve a satisfactory reaction of the reduced tin of the treated ore with the alkali metal hydroxide solution, the reaction should be conducted at a temperatureof at least 75 C. and,

. preferably, o'f-notless thanQO' C. The preferred reaction temperature is at or slightly belowthe boiling point of thealkali metal hydroxide Solution. After such treatment manna tin :may -be recovered by any of several methods, as 'hereinafter explained. v

The process herein contemplated is effectivefor treatment of all typesoftin ores containing'from as little as 5 percent, and up to 60 .per cent and even more of tin, including botHhighfg'ra'de and low grade ;ores. In the case .ofthe treatment of thehigh-tin ores such as ores .containingfabo've about 35 to 40 .per cent of tin, itis desirable in somecases to add an inert'malterial such as the spent residues from the leaching. operationh'e'reinafter described to .prevent, coalescence .offlthe tin during reductiontoas great an extent-as possible, and thereby make possible the-recovery .of a'better product. v

I The process of my invention is especially adapted to the treatment of low {grade tin concentrated or unconcentrated ores containing from about 15 to 35 per cent or less of tin, which have not been capable of commercial treatment prior tothe present invention. Such oresoften contain 5 per cent ormore of iron in addition to silica, arsenic, antimony, sulphur, etc. .Iftsulphur is present inan excessive amount, say about 2 per cent or more, it maybe desirableinsome Application- September 6, 1945, .Serial No. 614,825

cases to roast "the ore in accordance with conventional procedures'prior to treatment in order to eliminate all or a "portion of this material, thereby raisin'gthe fusion point, of the ore and preventing build-up of the sulfate in the'hereinafter described leach liquors. On the other hand, ores containing'small quantities of sulphur may be treatedwithout roasting, since some quantity of sulphur is'removed duringthe reduction treatment.

The reduction treatment of the ore may be effected by heating'the ore in a pulverized state, for example, minus 100 or 200 mesh, in the presenCe of a carbonaceous reducing agentsuch-a's coal, charcoal, carbon, coke, carbon monoxide, natural gas,water gas, etc.,-'in order to convert the tin content of'th'e'ore toastate in whichitis capable of reacting'wit'h an aqueous solution of an "alkali metal hydroxide. This treatment shouldbe' conducted at atemperaturesufliciently high to permit a major part'or all-0f thetin content of the ore to be "converted to the afore-- said state; however, thetemperature should not .be sohigh 'that'substantial fusion occurs and a molten'pooltof ore, slag or metallic'tin or other molten material is formed. A ball mill or other suitable grinding device may be employed'togrind the ore 'to the .desired'finely divided state. The,

' ore may be ground "tominus or 60 mesh, but

better yields of reactabletin are obtainedif the ore is ball-milled to therneshabove stated. p

The exacttemperaturewhich may beutilized in the reducing treatment is dependent'largely upon ,the nature of the ore .subjectedto'reduction. a veryserious extent at a temperature of about '1600 F. On the other hand, other Bolivian ores and'inany'Mexic'an ores maybe subjected. to temperatures as high as about.1800 orl1900 F. with out encountering Jserious fusion. Primarily the ore should be reduced at a temperature "such that ;a .material is produced" in whicha major portionof the tin may be convertedito a water .solubles'tannate by reaction withan aqueou'ssolution ofan alkali metalhydroxide. The reaction is preferably carried out in the presence of an 7 oxidizing. agent capable of oxidizing metallic tin in an alkalinetmedium, as hereinafter described. Slig htamounts of fusion resultingin some sintering of .-the orefundergcing treatmentmay betolen atedvin most cases. .On the other hand, fusion to an extent such that pools of molten material are formed is detrimental and should be avoided.

In generaL satisfactory results are usually ob tained .within a temperature'range of about-1400 or 1500 to about .2000 F. and for most tin ores a temperature affrom about .1600 to 1900" F. is most effective. A.,preferred temperature range i from.-about 1650 to ;1850 i a I The reducing agent used in effecting-reduction Thus, some Bolivian 'oresfuse or melt to carbon monoxide, water gas, hydrogen or natu v granular mass containing tin in dispersed small ral gas, and solid reducing agents may be, used,

as pointed out above.

I have been able to secure particularly effective results by conducting "the" reduction of the finely ground ore in the presence of a solid carbonaceous material, preferably in powdered form and preferably of a meshcorresponding substantially to the mesh of the ore.

These solid carbonaceous reducing agents are pro-1 ferred because they are easier to handle and because they have the property of minimizing fusion and sintering of the ore. Solid carbonaceous materials containing both nonvolatile and volatile carbonaceous reducing agents, such as anthracite or bituminous coal, are most suitable for this purpose. Bituminous coal is preferred because of its relative cheapness and availability. The period of time over which the ore is subjected to the reducing treatment is capable of considerable variation, being largely dependent upon the activity of the ore undergoing treatment and the temperature of treatment. Generally speaking, the time required is shorter wherethe temperature is high than where a lower temperature is used. In any case, however, unduly prolonged heat treatment of the ore is detrimental and should be avoided. The actual optimum time at the reduction temperature is usually quite short and usually doe not exceedab'out 30 to 40 minutes forlow-grade ores. From data obtained by carrying out experiments inv a reduction furnace, it appears that low-grade ores may be reduced to a goodproduct in a matter of from about 8 to 12 minutes and even less. These figures inelude the time required to heat the ore up to the reduction temperature, which in typical instances was shown to bein the order of about 3 to 5 minutes. suitable furnace, such as a hearth type furnace, for. example; a multiplehearth. Wedge type fur na'ce,"or a rotary furnace.

V .Theam'ount of reducing agent utilized is, in general, dependent upon the temperature of treatment and the type of furnace in which reduction is effected. It has been observed that fusion of the ore may be substantially decreased The reduction maybe effected in any Following the reducing treatment the ore may be cooled in a nonoxidizing atmosphere to prevent 'reoxidationf of the tin. The reduced ore after this cooling treatment usually is in the form of a black or dark colored pulverulent or particles in a form soluble in an aqueous alkali solution. Sometimes the mass may be more or less clinkered or caked and may require pulverizing or grinding treatment, say to minus 100v or 200 mesh, 'prior to or'in conjunction with the "aqueous alkali treatment. In the preferred operation, the reduced ore prior to the aqueous alkali treatment should be in a finely divided state such as set forth above. The exact nature of the reducing reactions is not known, although it is possible that the tin is reduced to a finely divided metallic state, the particles beingseparated'by the excess coal and by other materials in the reduced ore. In any event, the treated ore is amenable to reaction with an aqueoussolu+ tion of an alkali metal hydroxide.

The ore after the reduction treatment may be subjected to any of several types of aqueous alkaline treatments. If desired, it may be treated with an aqueous solution of sodium'hydroxide under conditions such that a liquid extract of sodium stannate is produced. Alternatively, it may be subjected to treatment with an aqueous solution containing at least 15 per cent of sodium hydroxide or its equivalent of another alkali metal hydroxide, and, generally, not substantially more than 1.5 times the theoretical amount of the hydroxide required to react with the tin in the reduced ore, In such a case reaction of the aqueous alkali solution with the-tin in the ore occurs rapidly to form a substantially solid mass comprising sodium stannate crystals. This mass may then be extracted with water to dissolve the stannate and thereby to separate it from the gangue including iron and silicon impurities. Usually it is desi'rableto conduct this treatment in' the presence of an-oxidizing agent capable of oxidizing metallic tin in an alkaline medium,.such as sodium nitrate, sodium hypochlorite, potassium nitrate. hydrogen peroxide, etc., in order to assist or speed up the rate of reaction. Generally, when the aforesaid solutions of sodium stannate are to be electrolyzed,

and minimized when the process is conducted in the presence of 'an'excess of solid carbonaceous material such as carbon or 'coal'. In treatment from about 15 to 35 per cent of tin, not less "than about twice the amount of carbon or'coal rewhere the temperature is unduly high or the treatment unduly long because coking may occur. The minimium or theoretical amount of bituminous coal, for example, required for reduction of the tin in a typical'low-grade Bolivian ore of about 20 per cent tin content is about 5 per cent ofthe weight of the ore.

'of ores, particularly low grade'ores containing 5 to 7 moles of alkali metal hydroxide are used per mole of oxidizing agent.

I It is preferred that the treatment of the reduced ore, with thealkali metal hydroxide solution be carried out in a countercurrent operation, either batch or continuous. In such operations the concentrations of the alkali'metal hy-' droxide' may vary widely,-s ay from about 50 to 200 gms. per liter of solution. It is preferred to use some oxidizing agent such as NaNOa, for example, with the alkali metal hydroxide in a concentration of'at least about 10gms. per'liter of solution. A preferred aqueous alkaline treating solutionfor a countercurrent operation contains '130 gmsjNaOH-and 40 gms. NaN03-per liter of solution. In general, the amount of alkaline treating solution used should be such as to pro vide an excess of the alkaline reagent overthe theoretical requirements for-the conversion of the tin to the stannate form; for example, an excess of about 50 to 300 per cent, preferably about, to 150-per cent. With the preferred solution containing gms. 'NaOH and 40 gms. NaNO; per liter of solution, one liter will efiectively treat an amountof'orejcontaining up to about 100 gms. of tin;-

' conducted at 60 C.

. Example 4 The process of Exampl 2 was repeated, using a solution containing 200 grams of sodium hydroxide per liter of solution and maintaining the temperature approximately at the boiling point of the solution; The resulting solution contained 92 grams of tin per liter of solution after a 4 hour leach. Only minor quantities of tin were extracted when the leaching processvwas Although the invention has especial value for thetre'atment of ores, including naturally occurring minerals'containing tin, and ore concentrates, the invention may also be applied to the treatment of other tin oxide containing materials including chemically precipitated stannic oxide, tin oxide wastes, etc. 'While the invention has been described with particular reference to sodium hydroxide, other alkali metal hydroxides such as potassium or lithium hydroxide or mix turesthereof may be used if desired. It is not intended that the specific details of the illustrafive-embodiments of the invention shall be regarded as limitations upon the scope of the invention, except in so far as included in the accompanying claims. I claim: 1. In the method of recovering tin from a lOt grade tin ore containing a substantial amount of metallic impurities including iron and at least about 5% of tin in a form in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in the presence of an excess of a solid carbonaceous reducing agent at a temperature of at least about 1400 F. but below that at which the ore fuses underconditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution is produced, reacting the product of such treatment containing the said soluble tin with an aqueous solution of an alkali metal hydroxide at a temperature of at least about 75 C.,- so as to convert the tin to a water-soluble tin compound and effect solution thereof substantially uncontaminated with iron, and separating the resulting solution from the residual ore.

2. The method set forth in claim 1 wherein the .solid carbonaceous reducing agent -is present in an amount of 'fr'om 15 to 30%, based on the weight of the ore, said percentagevarying in direct pro-; portion to the tin content of the ore. 3. The method set forth in claim 1 wherein the solid carbon-aceous'reducingagent is present in an amount of from 15 to 30%, based on the weight of the ore, said percentage varying in direct proportion tothe' tin content of the ore, and'wherein the ore contains from 15 to 35% of tin. 4. In the method of recovering tin from a low grade tin ore containinga substantial amount of metallic impurities including iron and at least about 5% of tin in a for'm'in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in the presence of an excess of a solid carbonaceous reducing agent at a temperature of at least' about 1400 F- but below that at which the ore fuses under conditions such that reduced ore containing tin inidispersed small particles in a form soluble in aqueous alkali solution is produced, reacting the product of such treatment containing the said soluble tin with an aqueous solution of an alkali metal hydroxide and an oxidizing agent capable of oxidizing metallic tin, in an alkaline medium, at a temperature of at least about v75 0., so asitoconverttlie' tinto a water-soluble tin compound and effect solution thereof substantially uncontaminated with iron, and separating the from the residual ore.

metal hydroxide is sodium hydroxide.

6. The method set forth in claim 4 wherein the oxidizing agent is an alkali metal nitrate.

'7. 'The method set forth in claim 4 whereinthe oxidizing agent is sodium hypochlorite.

8. In the method of recovering tin from a low grade tin ore containing a substantial amount of metallic impurities including iron and at least about 5% of tin in a form in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in th presence of at least about 15% by weight of a solid carbonaceous reducing agent, based on the weight of theore, at a temperature of at least about 1400 F., but below that at which the ore fuses under conditions such that reduced ore containing tin in dispersed small particles in a form solublejin aqueous alkali solution is produced, and reacting the product of such treatment containing the said soluble tin with an aqueous solution of analkali metal hydroxide at a temperature of at least about 75 C., so as to convert the tin to a watersoluble tin compound which may be dissolved without solution of iron in objectionable amounts.

9. The method of claim 8 in which the ore contains from about 15 to 35% of tin.

10. In the method of recovering tin from a low grade tin ore containing a substantial amount of metallic impurities including iron and at least about 5% of tin in a iorm in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in the presence of at least about 15% by weight of a solid carbonaceous reducing agent, based on the weight of the ore, at a temperature of at least about 1400 F. but

below that at which the ore fuses under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution is produced, and reacting the product of such treatment containing the,

said soluble tin with an aqueous solution of an alkali metal hydroxide and an oxidizing agent capable of oxidizing metallic tin in an alkaline medium, at a temperature of at least about '75. C., so as to convert the tin to a water-solubleftin compound which may be dissolved without solution of iron inobjectionable. amounts. 11. In the method of recovering tin from a low 55 grade tin ore containing a substantialamount of metallic impurities including iron"'and at least about 5% of tin in a form in which it is in asub stantially aqueous alkali-insoluble state, the steps comprising heating suchore in the presence of at 0 least about 15% by Weight of a solid carbonaceous reducing agent, based on the weight of the ore; at atemperature of at least about 1400 F. but below that at which the orefuses under conditions such that reduced ore containin tin in .5 dispersed small particles in a form soluble in aqueous alkali solution is produced, and'reacting the product of such treatment containing the said soluble tin with an aqueous'solution of 'an alkali metal hydroxide and an alkali metal nitrate at a temperature of at least about C., soas to convert the tin to a water-soluble tin compound n of iron which may be dissolved without solutio in objectionable amounts,

12. In the method of recoveringtin ffrom a low V 75 grade tin ore containing a substantial amount of resulting solution.

5. The method set forth in claim 4 wherein the oxidizing agent is sodium nitrate and the alkali e u impurities including iron and at least a o t t n i No m inwnichi i m substantiallyaquegjus alkalieinsoluble state, the

steps comprising heatingsuch ore inthepresence of at least about %.,by weight of a solid car- .bonaceous reducing agent, basedlon the weight of temperature of at least about 75C., so as to convert the tin to a water-soluble tin compound which may be dissolved without solution of iron in objectionable amounts.

13. In the method of recovering tin from a low grade tin ore containing a substantial amount of metallic impurities including iron and at least about 5% of tin in a form in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in the presence of at least about 15% by weight of a solid carbonaceous reducing'agent, based on the weight of the ore, at a temperature of at least about 1400 F. but below that-at which the ore fuses under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution is produced, and reacting the product of suchtreatme'nt containing the said soluble tin with. an aqueous solution of an alkali metal hydroxide and hydrogen peroxide at a temperature of at least about 75 C., so as toconvert the tin to a water-soluble tin compound which may be d ssolved without solution of iron in objectionable amounts.

14. In the method of recover-ing tin. from a low grade tin ore containing a substantial amount of metallic imouritiesincluding iron and at least about 5% of tin in a form in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore the presence of I a solid carbonaceous re uci g agent ata tem-- perature above about =l600 F, but below that at which the ore fu es under conditions such that reduced ore'contain'i' g' tin in dispersed. small particles in a formsoluh e,inaoueous alkali solution is produced and reacting-the nroduc't of such.

tial quantity of inert components and at least about 15% f i in ai i wh it is in a su stantially aqueous ,alka rinsolublestate, the steps comprising heating such ore ina finely divided state in a reducing atmosphere at a temperature below that at whichtheorefuses under conditions su h that red ced or o ai n i persed small les ina for-m so uble in a ueous alkali so n produ ed, an ea t t product of treatment containing the said soluble tin with an aqueous solution of an alkali metal hydroxide, at a temperature of. at least about 75 (3.. so. to convert the 'tin to a water soluble tinbcomnound whichmay be dissolved without solution of iron in. objectionable amounts.

16. In the method of recovering tin from a low solution of iron soluble tin compound s s a ia l uncont minated th me an se about. '75 .C. and about the boiling no 1 said solution, so 'as to convert the tin t, a water ,soluble tincompoundand effects lut substantially uncontaminated with iron 10 grade tin ore containing a substantial amountof metallic impurities including iron and asubstantial ,quantitykof inert components and .atfleast about 5% of tin in a vform in which it is in a.

- substan tially aqueous alkali-insoluble state, the 7 steps comprising heating such more in a finely diyidedstate in a reducing atmosphere (at 'a temperature below thatat which the .ore fuses under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution is produced, reacting the roduct M u h treatment containin the. said soluble tin with an aqueous solution of an alkali metal hydroxide, .at aitemnerature or, at least about so asito sonv rtthe tin to a waterand eifect solution thereoi' ara'un me resulting solution from the residual ore.

L 1'7. In the method of recoverin ti om a low grade tin ore containing a Substantial amount of metallic impurities including iron andat least about 5% of tin .in a form in which it 'isjin' a substanti lly aq e u alkalhinfiali ble state, the te s ompr n heatin s c ar i he e enc of t least a ou wice the amount solid sarna eo duc g a ent e red fireduce th tin content of the 0 7.6, ata temperature of .at

least about 1.400" F. but below that at WhiQh the ore .fuses under conditions suchthatreduced ore containing tin in dispersed small particles in .a

d z agent a able o oxidiz n meta l c iii i a alkaline um, at a tempera ure i-at leas I about 15 (3., so as to convert the tin to a watersoluble .tin compound and ,efiect solution thereof substantially uncontaminated with iron, andse arating the resulting solution .irom the residual ore. I

18. In the method of recovering tin from a low gradestin ere containing asubstantial amount of -,rne a .i i pu ties includin on and at least about 5% f i l n a fo m in wh h it is in a ub an i l a ueo s al alis nso ubl .t e. th

steps mp h ating uch a e in a finel divided state. in the presehflie .Qf an excess of ,a powderedcarbonaceous reducin a ent at a ,temperature-of :at .leastabout 1,40,0" but below that at which the ore fuses under conditions such that ,reducedpre containing tin in dispersed small particles in a form soluble in aou-eous alkali solution is produced. cooling and pulverizing the r ced ore, reacting the product ofsu rtreatmentlc ntaining the said soluble tin withan ;agueo11s ,so luticn of an alkali-metal hydroxide and an xidizing agent capable of oxidizing metallic. .n n

et 3 c th an alkalinemedium, at a temnerature arating the resulting solution from the Q YG- I 19.. In the method-of recovering tin from low grade tin ore containing asubstantial amount of metallic impurities including iron and at, least about-5% of tin in. a form, in which i substantially aqueous-alkali-insolubl ate step comprising eatin such ore .a, ;1?1 ely a. idea s at in h "pre enc e eowd s bv ace us.re u in a em eta.

perature of at least about 1400 FQ but below that th reo 1 T vat which theiorejfuses'for about 3 to about 40 1 minutes, under conditions such that reduced ore containing, tin in dispersed small particlesin a line'medium, atfla temperature between about 75 l and about the boiling point of the said solution; so asto convert the tin to a water-soluble. tin compound and effect solution thereof substan- 1 tially uncontaminated with iron, and separating the resulting solution from the residual ore.

v 20. In the method of recovering tin from a low, 1 grade tin or'e containing a substantial amount of metallic impurities including iron and about 5 5 ,to 35% of tin in a form in which it is in a substan-l tially aqueous alkalieinsoluble state, the steps comprising heating such ore in a, finely divided state in a reducing atmosphere at a temperature of at least about 1400 F. but below that at which the ore fuses under conditions such that reduced ,ore containing tin indispersed small particles in a form soluble, in aqueous alkali solution is pro-' duced,,and reacting the product of such treatment containing the said soluble, tin :with an 1 aqueous solution of an alkali metal hydroxide,

at atemperature between about 75? C. andabout the boiling pointof the said solution, so as to convert the, tin to a water-soluble tin compound whichmay be dissolved without solution of iron in objectionable amounts.-

. 21. In the methodof recovering tin from a low gradectin ore containing a substantial amount of metallic impurities includ ng iron and about 5% I to 35% of tin in a form in wh ch it is in a substantially aqueous alkali-insoluble state, the steps comprising heatingsuch orein a finely divided state in a reducing atmosphere at a temperature of at least about, 1400 F. but'below that at which the ore fuses underconditions such that reduced ore containing tin'ingdispersed small particles, in ,a form soluble in aqueous alkali solution is pro- .duced, andreacting. the product of such treatment containing. the, said soluble tin with an aqueous solution of an alkali metal hydroxide and an oxidizing agentjcapable of oxid zing metallic tin in an alkaline medium, at a temperature be- .tween about 75 C. and about the boiling point V soluble ,tin compound which may be dissolved without'solution of iron in objectionable amounts.

23. In the method of recovering tin from a low grade tin ore containinga substantial amount of metallic impurities including iron and at least about 5% of tin in a form in which it is in a substantially aqueous alkali-insoluble state, the steps comprising heating such ore in a finelydivided state the presence of a powdered carbonaceous reducing agent at a temperature of at least about 1 100. F. but below that at which the ore fuses 7 and reacting the product of such treatment containing the said soluble tin with an aqueous 'solution of an alkali metal hydroxide and an oxidizing agent capable of oxidizing metallic tin in an alkaline medium, at a temperature of about the boiling point of the said solution, so as to convert the tin to a water-soluble 'tin compound which may be dissolved without solution of iron in objectionable amounts.

24. In the method of recovering tin from a low grade tin ore containing a substantial amount of metallic impurities including iron and at least about 5% of tin in a form in which it, is in a substantially aqueous alkali-insoluble state, the steps comprising heating such orein a finely divided state in the presence of apowdered carbonaceous reducing agent at a temperature of at least about 1400 F. but below that at which the ore times under conditions such that reduced ore containing tin in dispersed small particles in a form soluble in aqueous alkali solution is produced, and reacting the product of suchtreatment containing the said soluble vtin with an of thesaid solution, so as to convert the tin to u a water-soluble tintcompound which maybe dissolved without solution 01 iron in objectionable,

amounts. v

1 a 522., Inthemethod ofrecovering tin from a low grade tin ore containinga substantial amount of Qmetallic impurities including iron and about 5% to 35% of tin in a form in which it is ina sub- 6 0 I stantially aqueous'alkali insoluble state, the steps comprisingpheating such or in a finely divided 1 state in a reducingatmosphereat a temperature .Of at'least about 1400" F. but below that at which Y theor'e fuses under conditions such that reduced ore containing tin in dispersed smallparticles in Qaiorm soluble in aqueous alkali solution is pro duced, cooling and pulverizing the reduced ore 1 n and reacting the product of such'treatment con.-

taining the said soluble tin with an aqueous solu- I tionfof analkali metal hydroxide and an oxidizing alkaline medium, ata temperature between about prior application 469,373. referred to in this patent; Y

UNITED STATES PATENTS 7 Number' Name 7 V Date- 1,902,735 Tamaru et a1 Mar. 21, 1933 883,589 Thirot f .Mar. 31,1908 1,018,734 Weber Feb 27, 1912 1,511,590 Buttfie'ld "Oct. 14, 1924 859,566 Leitch July 9, 1907 1,670,307 Little* May 22, 1928 2,055,732 Schertel Sept. 29, 1936 FOREIGN PATENTS Number Country Date 9,821 British June 14, 1889 10,309 British May 2,1906 984 British 5 A. D. 1853 614 British '.l A. D. 1915 OTHER REFERENCES 5 ,agent capable of oxidizing metallic tin in an 1 aqueous solution of an alkali metal hydroxide and an oxidizing agent capable of oxidizing metallic tin in an'alkaline medium, at a temperature between about C. and about'the boiling point of the saidsolution, so as to convert the tin to a water soluble tin compound which may be dissolved Without solution of iron in objectionable amounts.

u I IRvINGnMUsKar REFERE C S CITED Tm, by c. L. Mantell, The Chemical'C'atalog 00., N. Y., 1929, pp. 123, 124; 130, 133,138, 14

144, 265, 339, 340. (Copy in Div. 3.)

The following references. are of record the 

